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foundations of mathematics

...dominant views prevailed: realism, from the Latin
res (“thing”), which asserts that universals have an extra-mental reality—that is, they exist independently of perception;
conceptualism, which asserts that universals exist as entities within the mind but have no extra-mental existence; and nominalism, from the Latin
nomen (“name”), which asserts that...

nominalism

Ockham’s
conceptualism won few converts among medieval philosophers. But
conceptualism of one sort or another, combined with nominalism, was central to the philosophies of the 17th- and 18th-century British empiricists John Locke, George Berkeley, and Hume.

realism

In the medieval period, defenders of a broadly Aristotelian realism, including William of Shyreswood and Peter of Spain, were opposed by both nominalists and conceptualists. Nominalists, notably William of Ockham, insisted that everything in the nonlinguistic world is particular. They argued that universals are merely words which have a general application—an application which is...

...thought that Forms were really there, although only as embodied in particular instances. More skeptical philosophers denied the reality of universals altogether, some identifying them with thoughts (conceptualists), others with mere names (nominalists).